How Structural Batteries Just Got 10X Better

Author: Matt Ferrell

When is a battery more than just a battery? That’s not a riddle. A battery is more than a battery when it’s also a wall… or a floor, or even part of your car, or a plane. But what if that same battery could cut a laptop’s weight in half or slim your phone down to the thickness of a credit card? That’s the mind-bending potential of structural batteries, which combine energy storage and structural support into a single material. It’s a wild idea that could reshape how we build electronics, vehicles, and even aircraft — if we can make it work. Designing something that satisfies the needs of a structure and a battery is not easy. Is the juice worth the squeeze?

So, a structural battery is pretty much exactly what it says on the tin. It might sound like some kind of architectural power cell from a sci-fi movie, but it’s as simple as a device that works both as a battery and as a load-bearing part of a structure. In other words, it’s pulling double duty: holding energy and holding things together.

A great example of this is a team from Korea Advanced Institute of Science and Technology (KAIST) created a carbon fiber composite that’s not only strong enough to support serious weight, but also stores energy like a battery. It’s thin, lightweight, and packs in way more carbon fiber than previous designs, thanks to some clever resin work and high-pressure molding. If this hold s up, it could reshape how we build everything from EVs to airplanes.

What is a Structural Battery?

But for now, we’re mostly zooming in on mobility applications: think electric vehicles and aircraft. Why? Because in those cases, batteries and structural frames are usually two of the heaviest components. If we can fuse them together in a clever way, we can shave off a ton of weight. That means getting two components for the weight of one.¹

Through some slightly hand-wavey calculations, structural batteries are said to have their mass “disappear” into the mass of the structure itself. That’s why they’re sometimes marketed as “massless” batteries. I fell into that trap a few years ago. Of course, they’re not actually massless, so the term is misleading, and I’m going to stay away from it (this time around).²

The heavier something is, the more energy it takes to move it. And since more powerful batteries are usually bigger and heavier, you end up in a loop: more weight needs more power, which adds more weight. It’s the same trap as the “Tyranny of the Rocket Equation” — remember that headache from our previous episodes?³ Even a small weight savings can help ease the cycle.

It sounds like the ultimate tech hack… until you realize the hidden risks that come with it.

The Problem

As you might guess, actually pulling that off is way easier said than done. Developing materials that work well as both structural elements and batteries is way more complex and time-consuming than just focusing on one or the other. We’re not exactly building cars out of AA batteries.

So, there’s a lot to juggle — performance, safety, weight, cost — and that balancing act can lead to higher production costs and longer development cycles.⁴

One big hurdle is that batteries tend to swell as they charge, thanks to what’s known as the lithiation process. That’s when lithium ions move into the battery’s electrode materials during charging, causing them to physically expand. That’s already a problem in standard lithium-ion cells, but if your battery is also the floor of your car… well, you probably don’t want the only thing between you and the road warping and weakening under your feet.⁵

Oh, and let’s not forget about dendrites, those nasty little metal spikes that can form inside batteries and, if left unchecked, grow large enough to puncture the internal layers. Great for horror movies, terrible for structural integrity.⁶

And speaking of structural integrity: if your car’s frame is made of batteries, those batteries need to be tough. They’ve got to withstand accidents without bursting into flames, and they need to handle real-world conditions like constant vibration, temperature swings, torsion, shearing…basically, all the weird physical stress that comes with normal driving.⁵

On top of that, structural batteries need to last. You really don’t want your power source dying and having to replace the entire undercarriage of your car. That would be… less than ideal.⁵ And finally, if you want to see these things on the market, any solution needs to be affordable, scalable, and easy to manufacture.⁷

Despite all those challenges, some automakers have already managed to integrate structural batteries into mass production. Aircraft? That’s a whole different beast. But we’ll get to that.

First, let’s take a look at how researchers are tackling these issues and breaking through some of the biggest barriers. So, what kind of advancements are we seeing in the world of structural batteries?

The New Advances

So, what kind of advancements are we seeing in the world of structural batteries? Well, one notable breakthrough comes from the team at the Korea Advanced Institute of Science and Technology (KAIST) that I mentioned before. They’ve developed a thin, uniform, high-density structural battery made from a multifunctional carbon fiber composite.

The researchers’ approach centered on improving the interface and curing behavior of the materials involved. After a lot of testing, they settled on a combo of simple epoxy resin and a much less simple carbonate electrolyte-based solid polymer electrolyte. The epoxy brings the muscle — easy to shape and known for its strong mechanical properties — while the solid polymer electrolyte serves as the actual electrolyte, a.k.a. the lifeblood of the battery.⁸

Now, if you’ve ever worked with resin yourself, you probably know it has a tendency to trap air bubbles while curing. In this context, that’s a double whammy: bubbles reduce both the battery’s efficiency and the material’s structural integrity.⁹ However, if you can tightly control the temperature and the pressure (vacuum) during curing, the air bubbles are allowed to escape.

The KAIST team closely studied the resin’s curing process by examining both temperature and pressure’s effects on curing. They were able to minimize trapped air and optimize the final structure. The result? A high-density, multi-functional structural battery, manufactured using vacuum compression molding, a common technique that uses heat, pressure, and vacuum to shape materials while maintaining excellent strength and consistency.⁹

And it paid off. Their method reportedly boosted the volume fraction of carbon fibers by over 160% compared to previous carbon fiber-based batteries.⁹ That’s a serious upgrade in both form and function.

Last time we talked about structural batteries, we spent a lot of time with Leif Asp’s team from the Chalmers University of Technology in Sweden. And since then, they haven’t been sitting still. The team has continued to push the boundaries of structural battery design, refining their approach with carbon fiber composites and resin.

These composites are stiff, lightweight, and already well-suited for structural use, so it’s a strong foundation — literally. In their design, the carbon fibers pull double duty as both electrodes and current collectors, while a structural electrolyte allows ions to move through the battery just like you’d expect. Nothing radically new in what the battery is made of, but how they make it is where things get interesting.

The Chalmers team developed a technique that distributes the resin more evenly throughout the composite. This results in a material that they claim is not only energy-dense enough for commercial use, but also strong enough to rival aluminum.¹⁰ That’s a pretty sweet combo.

Previously, their structural battery reached an energy density of 24 Wh/kg, or about 20% of what a typical lithium-ion battery delivers. Now? They’ve pushed it up to 30 Wh/kg.¹¹ Still not close to lithium-ion, sure, but that’s a solid jump in just a couple of years.

And what does that mean in the real world? According to the team’s estimates, this kind of battery could cut a laptop’s weight in half, slim a smartphone down to the thickness of a credit card, or even boost the range of an electric car by up to 70% on a single charge.¹²¹³ I want to stress, though, that those are just estimations. Testing could very well yield some very different results. Still, as the saying goes, “big if true.”

And structural batteries aren’t just limited to consumer electronics and EVs. As we mentioned last time, a small but growing number of researchers think they could be the key to finally electrifying air travel. One of those researchers is Emile Greenhalgh and his team at Imperial College London.¹⁴ They’re developing a structural supercapacitor–C-beam combo specifically for aircraft.

Their prototype measures 80 cm long, 20 cm wide, 10 cm deep, and just 7 mm thick, and it includes two stacks of four structural supercapacitors, each measuring 30 × 15 × 0.5 cm. Like many structural energy devices, it’s built from carbon fiber — specifically, carbon fiber fabric electrodes reinforced with high-surface-area carbon aerogel. According to the team, that combo gives their device a solid balance between capacitance and structural strength.¹⁵

So why a supercapacitor instead of a traditional battery? Two main reasons. First, supercapacitors are just easier to work with. They’re less finicky and tend to have longer cycle lives. Second, many aircraft already use banks of supercapacitors to power critical emergency systems, like automatically opening the passenger doors during an emergency.

The catch? Most planes land safely (thankfully), so those supercapacitors spend 99% of their time as dead weight. Sounds like the perfect job for a structural energy device. Replace the C-beam in the fuselage with a structural supercapacitor, and now you’re saving weight, preserving safety features, and reducing emissions all in one go.

While Greenhalgh’s team first made headlines in 2023, they successfully demonstrated their structural supercapacitor in exactly this kind of application just last year.¹⁵ That’s a promising sign of what’s to come.

The Outlook

So that’s all very interesting. But how close are structural batteries to actually hitting the market?

Well, there’s good news… and there’s bad news.

The good news: several automakers have already incorporated structural batteries into commercially available vehicles. Tesla — for whatever that’s worth these days — has begun integrating structural battery packs into the frames of both the Cybertruck and Model Y.¹⁶ Even a few years back, Elon Musk called structural batteries “the right overall architecture from a physics standpoint,” though he also admitted they were “still far from optimized.”¹⁷

Then there’s BYD, which has been developing its own structural battery tech since 2020 with its “Blade Battery.”¹⁸ That’s a big deal. BYD is the world’s second-largest battery manufacturer (just behind CATL), and as of this year, they’ve officially surpassed Tesla as the top EV maker on the planet.¹⁹ So, yeah, structural batteries definitely have a toe-hold in the auto industry.

The bad news: most of the cutting-edge innovations we’ve covered today? Still stuck on lab benches. Progress is happening, but it’s unclear when these next-gen designs will make it into the next-next-gen of EVs.

And when it comes to aviation, the road…or runway…is even longer. Major players like Boeing and Airbus are currently more focused on biofuels and hydrogen than structural batteries.¹⁴ The aerospace world moves slowly, and cautiously.

Though electrifying air travel could open someone unexpected doors. Air travel is a major source of emissions, however, its also a a source of noise pollution.²⁰ As a result, there’s a lot of regulation on where and when planes can land or take off, and what paths they can take. With electric planes, however, the noise issue is greatly reduced. Potentially allowing more flights to land at more times, unlocking new travel routes and making it less of a a headache to live near an airport.²¹

But I’m getting ahead of myself. Where do structural batteries fall on NASA’s Technology Readiness Level (TRL) scale? It’s a bit of a mixed bag. The fact that structural batteries are already shipping in real consumer vehicles technically bumps them to TRL 9: fully proven systems in operational environments. But there’s still a lot of room for optimization, and we’re a long way off from seeing them become standard-issue across the entire EV market.

As for aerospace applications? That’s more like a TRL 5: validated in lab settings, but not yet tested in real-world conditions.²² The bottom line is, structural batteries still have a long way to go before they reach their full high-flying potential.